1. Field of the Invention
The present invention relates to a display device, and more particularly to a technique which is effectively applicable to an electroluminescence display device adopting organic electroluminescence elements.
2. Description of the Related Art
Recently, an electroluminescence display device adopting organic electroluminescence elements has been attracting an attention as a next-generation flat display device which is capable of replacing a CRT (cathode ray tube) and a liquid crystal display device. The organic electroluminescence display device is described as an organic EL device in an abbreviated form and is also referred to as an organic light-emitting diode display device and hence, the display device is hereinafter specified as an OLED display device which is an abbreviation of the latter device, that is, an organic light-emitting diode display device in this specification.
To compare with the current flat display device such as the liquid crystal display device or the like, the OLED display device has several features including (1) a feature that a voltage necessary for emitting light is low, that is, equal to or less than 10V and hence, the power consumption can be made small, (2) a feature that the OLED display device is of a self light emitting type and hence, a backlight is unnecessary, (3) a feature that a vacuum structure which is necessary in a plasma display device which is also of a self light emitting type is unnecessary in the OLED display device and hence, the OLED display device can be made light-weighted and thin and (4) a feature that a response time is short, that is, several μ seconds and hence, the OLED display device exhibits a wide viewing angle of equal to or more than 170 degrees.
Such a technique is described in, for example, a following patent-unrelated literature (1).
Patent-unrelated Literature (1):
                “Acquire a basic patent on a circuit aiming at the higher definition of an organic EL panel” (Nikkei Electronics, 2000.4.24 (no. 768), pp. 163 to 170, Apr. 24, 2000).        
Further, structures on which the above-mentioned organic electroluminescence elements in the OLED display device are mounted are described in, for example, following patent literatures.
Patent Literature (1):
                Japanese Laid-open Patent No. 203954/1994 (JP-A-6-203954).Patent Literature (2):        Japanese Laid-open Patent No. 071771/1997 (JP-A-9-071771).Patent Literature (3):        Japanese Laid-open Patent No. 041067/1998 (JP-A-10-041067).Patent Literature (4):        Japanese Laid-open Patent No. 134270/1998 (JP-A-2002-134270).        
Although the above-mentioned OLED display device is roughly classified into a single matrix type OLED display device and an active matrix type OLED display device due to shapes of an anode and a cathode, these OLED display devices have the same basic structure with respect to an OLED display element.
FIG. 9 is a cross-sectional view showing the basic structure of the OLED display element.
As shown in FIG. 9, the OLED display element is constituted by laminating an anode 11 formed of a transparent electrode which is made of ITO (Indium Tin Oxide) or the like, a hole-transporting layer 12, a light emitting layer 13, an electron-transporting layer 14 and a cathode 15 onto a glass substrate 10 in the order described above.
When a voltage is applied between the anode 11 and the cathode 15, positive holes implanted from the anode 11 and electrons implanted from the cathode 15 are coupled again in the inside of the light emitting layer 13, organic molecules which form the light emitting layer 13 are excited to produce excitons, then light is emitted from the light emitting layer 13 in a process that the excitons are subjected to the radiation deactivation, and the light is emitted to the outside from the transparent anode 11 through the glass substrate 10 thus performing the light emission.
Hereinafter, a multi-layered film constituted of the hole transporting layer 12, the light emitting layer 13 and the electron transporting layer 14 is referred to as an OLED film 30.
In the single matrix type OLED display device, the anode 11 and the cathode 15 shown in FIG. 9 are respectively constituted of a large number of stripe electrodes which cross each other at a right angle while sandwiching the OLED film 30 therebetween. A driving voltage is applied to pixels which are arranged at crossing points of a large number of stripe electrodes which constitute the anode 11 and a large number of stripe electrodes which constitute the cathode 15. To compare the single matrix type OLED display device and a single matrix type liquid crystal display device (for example, a passive matrix type liquid crystal display device known as a STN type liquid crystal display device), while a group consisting of a plurality of common electrodes (a group of first stripe electrodes) and a group consisting of a plurality of segment electrodes (a group of second stripe electrodes) are respectively mounted on a pair of substrates which are arranged at both sides of a liquid crystal layer in the latter, the group of first stripe electrodes and the group of second stripe electrodes are respectively mounted on both sides of the above-mentioned OLED film which is formed on a main surface of one substrate in the former.
Further, in the active matrix type OLED display device, the anode 11 is formed for every pixel and a driving voltage is applied to the anode 11 by way of an active element, for example, a TFT (Thin Film Transistor) which is provided for every pixel. To compare the active matrix type OLED display device and an active matrix type liquid crystal display device, the above-mentioned anode 11 of the former corresponds to a pixel electrode of the latter and the cathode 15 of the former corresponds to a counter electrode (common electrode) of the latter.
Irrespective of the difference between the passive matrix driving method and the active matrix driving method, there may be a case that the OLED film 30 of the above-mentioned OLED display device includes at least the light emitting layer (organic material layer which exhibits an electroluminescence phenomenon) 13 and does not include the above-mentioned hole transporting layer 12 and the above-mentioned electron transporting layer 14.
FIG. 10 is a schematic cross-sectional view showing the structure of a conventional OLED display device.
The OLED display device shown in FIG. 10 is constituted of a glass substrate 10 which forms a display surface and a sealing can 20 which is adhered and sealed to the glass substrate 10 using an adhesive agent 21. Here, the adhesive agent 21 is made of ultraviolet curing type resin.
An anode 11, an OLED film 30 and a cathode 15 are formed on the glass substrate 10, wherein the OLED film 30 is formed of a multi-layered film which is constituted of a hole transporting layer 12, a light emitting layer 13 and an electron transporting layer 14. In other words, the OLED display device shown in FIG. 10 is provided with the laminated structure ranging from the anode 10 to the cathode 15 shown in FIG. 9 for every pixel.
Light emitted from the light emitting layer 13 of the OLED film 30 is irradiated to the glass substrate 10 side as indicated by an arrow in FIG. 10.
Further, the sealing can 20 is made of metal such as stainless steel. As shown in FIG. 10, a recessed portion 22 is formed in a portion of the sealing can 20 and a drying agent 23 is fixedly housed in the recessed portion 22 using a tape 25. The recessed portion 22 is provided at an approximately center portion of the sealing can 20.
Further, in a sealing space 26 which is surrounded by the sealing can 20 and the glass substrate 10, a dried and inert gas (nitrogen gas, for example) is sealed.
In the single matrix type OLED display device shown in FIG. 10, one of a plurality of stripe electrodes which constitute the anode 11 is shown as a thin film which extends in the lateral direction in FIG. 10 and cross sections of a plurality of stripe electrodes which constitute the cathode 15 are indicated such that they are arranged in parallel in the lateral direction. In other words, the plurality of the above-mentioned anodes 11 are arranged in parallel and the plurality of the above-mentioned cathodes 15 extend along the normal direction of FIG. 10. In this manner, the plurality of anodes 11 and the plurality of cathodes 15 are formed on the main surface of the glass substrate 10 such that they cross each other at a right angle while sandwiching the OLED film 30 therebetween.